The impact of different types of extreme temperature events on mental disorders: A case-crossover study in Anhui Province, China

Background: Extreme temperatures are expected to be more frequent, intense, and complex in the context of climate change. However, epidemiologic evidence about associations between extreme temperature and mental disorders is limited. Methods: We conducted a case-crossover study in Anhui Province, China, focusing on outpatients diagnosed with mental and behavioral disorders (ICD-10 codes: F00-F99), further classified into schizophrenia (F20-F21), depression (F32-F33), and anxiety (F40-F41). Defining the day of each outpatient visit to the Anhui Mental Health Center as the case day, a total of 762,895 case days and 3,362,574 control days were included in the study, covering the period from 2019 to 2021. Each subject was geocoded based on their home address and matched with environmental exposures, including meteorological data and air pollutant data sourced from the CN05.1 and the TAP dataset, respectively. Extreme temperature events were categorized into heat and cold extremes, further divided into daytime, nighttime, and compound extremes. Results: Among the outpatient visits for mental disorders included in this study, the proportions were schizophrenia (28.9 %), depression (23.9 %), and anxiety (18.5 %). Exposure to extreme heat and cold was associated with increased risks of outpatient visits for mental disorders, with odds ratios (ORs) of 2.23 (95 %CI: 2.16-2.30) and 1.95 (95 %CI: 1.89-2.01), respectively. Compound heat extremes posed the highest risk of mental disorders (OR = 1.17, 95 %CI: 1.13-1.22), followed by nighttime (OR = 1.11, 95 %CI: 1.08-1.14) and daytime heat (OR = 1.05, 95 %CI: 1.04-1.07). Notably, the risk of mental disorders significantly elevated with the increased intensity and duration of extreme heat events. Besides, extreme heat was strongly associated with higher risks of depression, schizophrenia and anxiety, while extreme cold was notably linked to schizophrenia. Conclusion: These findings indicate a significant correlation between extreme temperature exposure and elevated mental disorder risks, emphasizing the urgent need to address increased mental health risks posed by extreme temperatures in the changing climate.